Printed circuits are widely used as an inexpensive vehicle for interconnecting various electronic components in an electronic circuit. It is known in the art to produce printed circuits by a so called "build-up" method, wherein an insulating carrier or base material is clad with a relatively thin base layer of copper. A mask or pattern is provided over the base layer of copper to cover all areas not corresponding to the desired pattern of the printed circuit. The unmasked, exposed copper is then "built-up", typically by means of galvanic or electrolytic deposition of copper, and if desired, additional metals such as tin/lead alloys, nickel, brass, gold and the like. Thereafter, the layer of masking material is removed and the original thin layer of previously masked copper, which is now exposed, is removed by an etching treatment. Heretofore, printed circuits produced by the "build-up" method were typically made in batches wherein a limited amber of insulation boards were simultaneously masked, built-up and etched in individual deposition tanks and etching tanks.
Efforts have been made to produce printed circuits by automatic, continuous fabrication wherein dry photopolymer material is applied to and masks selected portions of a copper clad, continuous length of flexible polymer strip to form patterns of exposed copper thereon. The copper clad strip is guided over a cathodic electrode roller into a copper plating bath. Portions of the exposed copper contact the electrode roller and couple the cathodic potential thereof to the bath wherein an anode adjacent the strip affects plating of copper from the bath onto the exposed selected portions of the copper.
A problem with such processes is that the current which may be applied to the film, is limited by the cross-sectional area of the base layer of copper thereon. In this respect, it is the layer of copper on the film which conducts current from the cathodic electrode roller to the plating tank. In addition to the cross-sectional area of the copper layer, i.e. the width of the copper layer times (x) its thickness equalling the current carrying cross-sectional area of the metal, the distance from the cathodic electrode rollers to the plating tank also affects the current carrying ability of the copper layer. In this respect, it is well known in the art that the longer the current path, the greater the resistance to current flow, and that heat generated in the foil increases by the square of the current. The damaging effect of heat on copper foil as well as the processing equipment represents a major obstacle to the continuous processing of printed circuits. Thus, the thinner the base foil, the less current which may be applied to the foil.
The present invention overcomes limitations in continuous processing by providing an apparatus which shortens the current flow path between the cathodic electrode and the anode electrode and effectively increases the cross-sectional area of foil to which current may be applied.